1. Field of the Invention
The invention relates to a heat exchanger for at least one thermoelectric thin-film or thin layer element with a hot side and a cold side that extend along opposite long sides of the thin-film element, wherein the hot side is connected by a connecting element to a heat source and the cold side is connected to a heat sink.
2. Related Art
A thermoelectric generator can convert heat directly into electrical energy. Variously doped semiconductor materials are preferably used for this purpose, as a result of which efficiency can be significantly increased over that of thermocouples with two different metals connected to each other at one end. The thermoelectric generators available today, however, have relatively low efficiency. The standard semiconductor materials are Bi2Te3, PbTe, SiGe, BiSb, and FeSi2 with efficiencies in the range of 3-8% To obtain sufficiently high voltages, several thermoelectric generators are connected electrically in series.
The way in which a thermoelectric generator works is based on the thermoelectric effect, referred to in the following as the Seebeck effect. The Seebeck effect refers to the production of an electrical voltage between two points of an electrical conductor or semiconductor which are at different temperatures. The voltage which occurs is determined by:USeebeck=α·ΔT. where:
ΔT is the temperature difference between the ends of the conductor/semiconductor or between the contact points; and
α is the Seebeck coefficient or the so-called “thermoelectric power”.
The Seebeck coefficient has the unit of an electrical voltage per temperature difference (V/K). The resulting voltage is independent of the ambient temperature and is dependent only on the temperature difference between the contact points. A thermoelectric generator of high efficiency is obtained in a material with a high Seebeck coefficient and with, at the same time, low resistivity and low thermal conductivity.
To increase the efficiency of a thermoelectric generator, a thermoelectric thin-layer element with at least one n-layer and at least one p-layer of a doped semiconductor has already been proposed in EP 1 287 566 B1, wherein the n-layer and the p-layer are arranged to form a pn-junction. The n-layer and the p-layer are contacted in an electrically selective manner. A temperature gradient is applied parallel to the boundary layer between the n-layer and the p-layer. The pn-junction is formed essentially along the entire the n-layer and p-layer, preferably along their longest dimension, and thus essentially along the entire boundary layer between them. As a result of the temperature gradient along the large pn-interface, a temperature difference develops between the two ends of a pn-layer package along this pn-junction of elongated form this temperature difference leads to a higher efficiency of the thermoelectric element than that known from the prior art, which comprises no temperature gradient along and within the pn-junction. The n and p-layers are contacted selectively either by producing an alloy in the contact areas and the associated pn-junctions or by direct contacting of the individual layers. The selective contacts are separate, that is, not conductively connected to each other, and are arranged on the p- and n-layers.
A thermoelectric thin-layer element with a support structure, on which several thermoelectric bars consisting of a first conductive material and several thermoelectric bars of a second conductive material are applied, is known from DE 10 2006 031 164. The first and second conductive materials have different conductivities, and the thermoelectric bars are electrically connected to each other such that two of them form a thermoelectric pair. The thermoelectric bars of the first and second conductive materials are arranged next to each other on the support structure. The cold side of the thermoelectric thin-layer element is located on one side of the electrically conductive first and second materials, and the hot side is located on the opposite side of the electrically conductive first and second materials.
A thermoelectric thin-layer element is known from DE 101 22 679 A1, which comprises a flexible substrate material, to which thin-layer thermoelectric pairs are applied. The thin-layer thermoelectric pairs are formed out of a material combination of two different materials. The first and the second material are arranged and thermally connected to each other such that, together, they form a thermoelectric pair. The two materials are printed onto the flexible film or deposited by conventional deposition methods. Strips of, for example, nickel as the first material and strips of chromium as the second material are arranged next to each other. The webs and strips are connected in pairs electrically to each other at their ends by a connecting structure of the second material. As a result of the connected webs and strips, a series circuit of several thermoelectric pairs is formed on a small surface. The large number of thin-layer thermoelectric pairs leads to a high output voltage of the thermocouple. The electrical connecting structures on the one side of the thermoelectric thin-layer element form its hot side, whereas the connecting structures on the opposite side of the thermoelectric thin-layer element form the cold side, wherein the hot side is connected by a connecting element to a heat source and the cold side to a heat sink.